The present invention relates to valves and more particularly to a modulating control valve.
The described valve is especially suitable for application to control operation of a forward-reverse clutch. passage means
Use of modulating control valves to control hydraulic system operations has been known for some time. Numerous constructions for modulating control valves are known. For example, see the following patents, all assigned to the assignee of the present invention: U.S. Pat. Nos. 2,972,536 issued Feb. 14, 1961; 3,477,225 issued Nov. 11, 1969; 3,486,418 issued Dec. 30, 1969; 3,556,155 issued Jan. 19, 1971; and 3,862,645 issued Jan. 28, 1975. These patents exemplify the prior art approach to modulation control of either a main control valve or a hydraulic motor.
However, these problems and solutions differ from those encountered when considering control of a slippable torous friction clutch such as shown in U.S. Pat. No. 3,217,851 issued Nov. 16, 1965, also to the assignee of the instant invention. The difficulty encountered with controlling these clutches is the tendency to "stick slip" at some point in their application. Stick slip or damaging clutch torsionals always occur near the lock up point with sintered bronze clutches. With stick slip, severe clutch damage can occur if there is an extremely sudden lock up of clutch. This is, of course, very costly in terms of lost time and operation of the equipment with which the clutch is used.